Semiconductor wafers and chips are sometimes thinned for packaging processes. To thin a semiconductor wafer, a ultra-violet (UV) tape is adhered to a front side of the semiconductor wafer. A backside grinding is then performed to the backside of the semiconductor wafer, until the thickness of the semiconductor wafer reaches a desirable value. After the backside grinding, the UV tape is subject to a UV exposure using UV light, so that the UV tape can be removed from the semiconductor wafer.
In conventional UV exposure processes, a UV lamp is placed on a platform, with the UV light being projected upward. The UV lamp has a strip shape. The semiconductor wafer is positioned over the UV lamp, and is initially located at a position not subject to the UV exposure. The semiconductor wafer then moves directly over the UV lamp, so that the UV tape, which faces the UV lamp, is subjected to the UV exposure. The direction of the movement is perpendicular to the longitudinal direction of the UV lamp. The semiconductor wafer continuously moves forward, until it is no longer directly over the UV lamp. During the movement, the entire semiconductor wafer is subject to the UV light. After the UV exposure, the UV tape is removed from the semiconductor wafer.
In an alternative way of UV exposure, a UV lamp is placed facing upward, and the semiconductor wafer is positioned directly over the UV lamp, with the UV tape facing the UV lamp. The UV tape is subject to the UV exposure for a certain period of time. During the exposure, the semiconductor wafer remains not moved. After the UV exposure, the semiconductor wafer is removed from directly over the semiconductor wafer, and the UV tape is removed from the semiconductor wafer.
In the conventional de-taping processes, portions of the UV tape may not receive adequate UV exposure. As a result, UV residue may be left on the semiconductor wafer. For example, the portions of the UV tape on edges of the semiconductor wafer are often not exposed adequately. Further, ball grid array (BGA) balls may be formed on the surface of the semiconductor wafer, and are in contact with the UV tape. BGA balls do not have vertical sidewalls, and portions of the BGA balls may block the UV light from being projected on some portions of the UV tape. As a result, the portions of the UV tape blocked from the UV light are also not exposed to UV light adequately. This cause residue of the UV tape to be left on the semiconductor wafer after the removal of the UV tape. The Residue of the UV tape may cause yield loss in subsequent packaging processes.